(1) Field of the Invention
The present invention relates to a control unit of a flash memory and a facsimile machine, such as a portable facsimile machine, having a flash memory for storing image data and the control unit of the flash memory.
(2) Description of the Related Art
A picture processor has been proposed in Japanese Laid Open Patent Application No. 3-179972 (a first reference). In this picture processor, when there is no idle area to record picture data in a memory, a recording operation is interrupted and the processor waits for protection of the recording operation to be canceled. When the protection is canceled, the recording operation automatically restarts. As a result, picture data is recorded in the idle area of the memory so that continuity of storage of picture data is maintained.
A facsimile machine has been also proposed in Japanese Laid Open Patent Application No. 3-177158 (a second reference). This facsimile machine is provided with a memory circuit for storing image data.
A flash memory, which is one type of rewritable non-volatile memory, is expected to be used as a large-capacity memory. A flash memory can be used, for example, as a memory for storing image data in a facsimile machine as disclosed in the second reference. In this case, the writing control of the flash memory can be performed in a manner, for example, as disclosed in the first reference.
However, if the writing control of the flash memory is performed so that image data is unmethodically stored in the idle area of the flash memory as disclosed in the first reference, the following disadvantages occur.
The number of rewrites (the rewritable number) of the flash memory generally is limited in a range between 10 thousands and 100 thousands. Thus, in a case where the flash memory is used as an image memory of the facsimile machine, the above limitation of the rewritable number of the flash memory must be considered. If the increase of the rewritable number is concentrated on only a part of the recording area in the flash memory, the part of the recording area becomes unusable sooner than other parts thereof. That is, the flash memory cannot be used for a long time under the maximum memory size. In this case, the flash memory in which the image data is to be stored overflows more quickly.